Kyohei Fujimoto

Design concept of antennas for small mobile terminals and the future perspective

With the progress and rapid increase in mobile terminals, the design of antennas for small mobile terminals is acquiring great importance. In view of this situation, the design concept of antenna systems for small mobile terminals and its future perspective are discussed, referring to the trends in modern mobile communications and the demands for the antenna system. The design concept of antenna systems has changed along with the progress of mobile systems. In the conventional design, the conducting material of the equipment case, existing near the antenna element, is included as a part of the radiator in the antenna system, without regard to whether or not it has been considered. In the latest mobile phones, the design concept has been advanced to aim at improving the antennas performance, and the treatment of the case, etc., has become a part of this. Some particular considerations for the design are to relieve the degradation of the antennas performance due to the human-body effect, to overcome the SAR problems, and yet to make the size small. Furthermore, it is now time to proceed to the more-advanced concept, in which implementation of adaptive control and software is considered, even in small mobile terminals. Typical trends in modern communications systems are discussed, and the demands of these trends-which are summarized as down-sizing, function, and intelligence-are taken up for future antenna structures. Small-antenna technology and the application of the integration technology to antenna systems are essential for realizing such future structures.

Analysis of a cavity-backed annular slot antenna with one point shorted

Analysis of a cavity-backed annular slot antenna with one point shorted is performed experimentally and theoretically. Resonance frequencies, bandwidths, and radiation patterns are studied with respect to slot width, cavity depth, and slot shorting position. In the theoretical analysis, the method of moments is applied to find the magnet current on the slot, and the Greens function for the field inside the cavity has been newly derived. By selecting a slot shorting position, circular polarization, and a bandwidth of more than 10%, the voltage standing-wave ratio (VSWR) >

Characteristics of a balance-fed loop antenna system for handsets in the vicinity of human head or hand

In this paper, in order to confirm the effectiveness of using the balanced antenna structure, the performance of the balance-fed antenna system for a handset under the influence of a human head or hand is analyzed numerically and experimentally. As a human head model, the COST (European Cooperation in the field of Scientific and Technical Research) 244 model, which has a spherical or cubic form, is used. The hand is simply simulated as the combined rectangular prism on the basis of the average size of human hands. The electromagnetic IE3D simulator by Zeland Software is used to obtain the antenna characteristics such as the current distribution and radiation pattern.

Experimental results with mobile antennas having cross-polarization components in urban and rural areas

The receiving performance of mobile antenna systems that have vertical and horizontal elements at the 920-MHz band has been investigated by measurements in both rural and urban areas in Japan. Three types of inverted-F antennas for a car and three types of antenna elements, a monopole, a bent-slot and an inverted-F antenna, for portable equipment were used in the experiments. The average received power and its probability density function are obtained as the parameter to evaluate the performance of antenna systems. The performances of the bent-slot antenna system for portable equipment and the inverted-F antenna system mounted on a car are compared with those of the monopole or dipole antenna systems used as reference antennas. A notable increase in the average received power has been observed in operation in an urban area where the field distributes randomly and consists of cross-polarized components. >

Antennas for Mobile Communications

Antennas used for mobile communications are not necessarily specialized types of antenna; ordinary antenna types can be used. However, there are several distinctions in performance between mobile and fixed communications with respect to design methodology for antennas in mobile communications, including variations of field strength, varied environmental conditions, mechanical and physical robustness, and mechanical and electrical system performance. Keywords: antennas; mobile; fixed; communications; base station

Signal bandwidth consideration of mutual coupling effects on adaptive array performance

The effect of mutual coupling on the performance of a least mean square (LMS) adaptive array using dipole elements is analyzed in consideration of the signal bandwidth. The purpose here is to illustrate quantitatively the significance of the effect of mutual coupling. The results show that the effect in the broad-band signal cases is much greater than that in the narrow-band cases, particularly when few antenna elements are used.

Characteristics of Built-In Folded Monopole Antenna for Handsets

A folded loop antenna for handsets has already been introduced and shown as one of balance-fed antennas for handsets, which is very effective to mitigate the antenna performance degradation due to the body effect. In order to meet the requirements for the latest handsets such as low profile and small size, a folded loop antenna is modified. The antenna, which is possibly built in the handsets, is newly proposed. Low profile and small size is achieved by consisting of the half of low profile folded loop antenna, which has a structure folded loop elements sideways so that the antenna can be placed on the ground plane (GP). In the analysis, the electro-magnetic simulator based on the FDTD (Finite Difference Time Domain) method is used and the design parameters useful in practical operation are found. The electromagnetic simulator based on the Method of Moment (MoM) is used to calculate the current distribution on the antenna element and the GP. An example of low profile and small size antenna which has wideband characteristics are designed based on these parameters, and the antenna characteristics such as VSWR, the current distributions and the radiation patterns are compared with Planar Inverted-F Antenna (PIFA), which is one of conventional built-in antennas for handset. As a result, it has been confirmed that the physical volume of the antenna, which has been introduced here, becomes smaller than that of PIFA. In addition, the radiation efficiency of these antennas is measured and the results are compared with each other.

UHF bent-slot antenna system for portable equipment—II: Receiving performance in urban areas

The receiving performance of UHF portable equipment with a bent-slot antenna is studied on the basis of experimental results. The received power increase in the experiment is analyzed by applying the ray and random models to urban area structures. The analysis shows that the bent-slot antenna designed with both vertical and horizontal polarization components has contributed to an increase in received power for some limited angles of wave incidence, as a result of combined reception of cross-polarized waves in an actual environment.

A balance-fed loop antenna system for handsets

Theoretical and experimental analysis of a newly proposed loop antenna for handsets is presented. A simple model, using a small rectangular and L-shaped loop antenna mounted on a ground plane, which represents a rectangular shielding plate used in the handset, is analyzed in order to confirm the effectiveness of using the balance-fed antenna system.

Three-dimensional performance of an LMS adaptive array with inverted-F elements

The performance of an adaptive array with two inverted-F elements is analyzed by using the method of moments. A random signal model for mobile communication in a typical urban area is used. Three-dimensional analysis is applied to give a clear expression of the array output signal-to-interference plus noise ratio (SINR) performance. Also, a factor called SINR pattern angle ratio (PAR) is introduced with which a quantitative evaluation of the SINR patterns becomes possible. By using the PAR, the array performance for different array parameters such as inverted-F antenna (IFA) element orientations, interelement spacings and incident signal directions are computed. As a result, the IFA element is found preferable to a quarterwave monopole array in the assumed signal environment. >